Electrode array for a cochlear implant having one or more adjustable electrodes

ABSTRACT

An electrode array for a tissue-stimulating prosthesis, such as a cochlear implant. The electrode array is comprised of a plurality of electrodes ( 41 ), wherein at least one electrode of the array is comprised of at least two electrically connected portions ( 41   a,   41   b ) that are adjustable in orientation relative to each other. This adjustability in orientation preferably allows the array to adopt a tighter curvature than would be the case were the electrode portions not relatively adjustable to each other.

FIELD OF THE INVENTION

The present invention relates to an implantable electrode array and, inparticular, a cochlear implant electrode assembly.

BACKGROUND OF THE INVENTION

Hearing loss, which may be due to many different causes, is generally oftwo types, conductive and sensor neural. In some cases, a person mayhave hearing loss of both types. Of them, conductive hearing loss occurswhere the normal mechanical pathways for sound to reach the hair cellsin the cochlea are impeded, for example, by damage to the icicles.Conductive hearing loss may often be helped by use of conventionalhearing aids, which amplify sound so that acoustic information doesreach the cochlea and the hair cells.

In many people who are profoundly deaf, however, the reason for theirdeafness is sensor neural hearing loss. This type of hearing loss is dueto the absence of, or destruction of, the hair cells in the cochleawhich transduce acoustic signals into nerve impulses. These people arethus unable to derive suitable benefit from conventional hearing aidsystems, no matter how loud the acoustic stimulus is made, because thereis damage to or absence of the mechanism for nerve impulses to begenerated from sound in the normal manner.

It is for this purpose that cochlear implant systems have beendeveloped. Such systems bypass the hair cells in the cochlea anddirectly deliver electrical stimulation to the auditory nerve fibres,thereby allowing the brain to perceive a hearing sensation resemblingthe natural hearing sensation normally delivered to the auditory nerve.

Cochlear implant systems have generally consisted of essentially twocomponents, an external component commonly referred to as a processorunit and an internal implanted component commonly referred to as areceiver/stimulator unit. Traditionally, both of these components havecooperated together to provide the sound sensation to a recipient.

The external component has traditionally consisted of a microphone fordetecting sounds, such as speech and environmental sounds, a speechprocessor that converts speech into a coded signal, a power source suchas a battery, and an external transmitter coil.

The coded signal output by the sound processor is transmittedtranscutaneously to the implanted receiver/stimulator unit situatedwithin a recess of the temporal bone of the recipient. Thistranscutaneous transmission occurs via the external transmitter coilwhich is positioned to communicate with an implanted receiver coilprovided with the receiver/stimulator unit. This communication servestwo essential purposes, firstly to transcutaneously transmit the codedsound signal and secondly to provide power to the implantedreceiver/stimulator unit. Conventionally, this link has been in the formof a radio frequency (RF) link, but other such links have been proposedand implemented with varying degrees of success.

The implanted receiver/stimulator unit traditionally includes a receivercoil that receives the coded signal and power from the externalprocessor component, and a stimulator that processes the coded signaland outputs a stimulation signal to an intracochlea electrode assemblywhich applies the electrical stimulation directly to the auditory nerveproducing a hearing sensation corresponding to the original detectedsound.

It is known in the art that the cochlea is tonotopically mapped. Inother words, the cochlea can be partitioned into regions, with eachregion being responsive to signals in a particular frequency range. Thisproperty of the cochlea has been exploited by providing the electrodeassembly with an array of electrodes, each electrode being arranged andconstructed to deliver a stimulating signal within a preselectedfrequency range, to the appropriate region within the scala tympani ofthe cochlea. The electrical currents and electric fields from eachelectrode stimulate the nerves disposed on the modiolus of the cochlea.

To achieve good positioning of the electrode assembly, it is desirablethat the array be inserted relatively deeply into the scala tympani ofthe cochlea and positioned as close as possible to the inner wall of thecochlea to enable direct stimulation of the appropriate auditory nervescells disposed in the modiolus of the cochlea. For this reason,electrode arrays having a shape adapted to conform to the shape of themodiolus of the cochlea have been developed, such as that described inthe Applicant's U.S. Pat. No. 6,421,569.

The present invention therefore assists in achieving this outcome toachieve optimal placement of the electrodes of the electrode array.

Any discussion of documents, acts, materials, devices, articles or thelike which has been included in the present specification is solely forthe purpose of providing a context for the present invention. It is notto be taken as an admission that any or all of these matters form partof the prior art base or were common general knowledge in the fieldrelevant to the present invention as it existed in Australia before thepriority date of each claim of this application.

SUMMARY OF THE INVENTION

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

According to a first aspect, the present application is directed to afirst invention comprising an electrode array for a tissue-stimulatingprosthesis, the electrode array comprising a plurality of electrodes,wherein at least one electrode of the array is comprised of at least twoelectrically connected portions that are adjustable in orientationrelative to each other.

This adjustability in orientation preferably allows the array to adopt atighter curvature than would be the case were the electrode portions notrelatively adjustable to each other.

In one embodiment, the electrode array can comprise one of a pluralityof stacked but laterally off-set electrode sets used for atissue-stimulating prosthesis.

In a further embodiment, the array is supported in a carrier member. Thecarrier member can have a leading end and a trailing end. The arraypreferably extends from a position at or adjacent the leading end backalong the carrier member towards the trailing end. In one embodiment,said at least one adjustable electrode is adjacent the leading end ofthe carrier member. In another embodiment, said at least one adjustableelectrode can be at a location where adjustability is more likely to berequired following insertion of the array. In one embodiment, the arraycan comprise adjustable electrodes interspersed between othernon-adjustable electrodes. In one embodiment, at least some adjustableelectrodes can be positioned side-by-side in the array.

Each adjustable electrode can comprise two or more portions. Eachportion preferably extends outwardly from a common conducting portion.In one embodiment, a gap can be present between the portions of theelectrode. In another embodiment, the gap can be bridged by one or morebridge members. In one embodiment, the bridge member can extend betweenthe portions at a location distal the common conducting portion. Each orsome of the bridge members can have a thickness equal to or differentthan that of the electrode portions. In another embodiment, the portionscan be linked by a region that fully or substantially closes the gap andwhich has a thickness less than that of the adjacent portions. In oneembodiment, the region that fully or substantially closes the gap canhave a substantially V-shaped cross-section, with the electrodepreferentially bendable at this location.

Each portion is preferably fabricated so as to be in a common plane andare then adjustable in orientation relative to this plane onimplantation of the array. Each portion of each said adjustableelectrode is preferably rectangular in shape, however any shape isenvisaged as being within the scope of the present invention. Respectiveportions of each said adjustable electrode are also preferably of aboutequal dimensions. It will be appreciated that the respective portionscould, however, be of different shapes and/or sizes compared to eachother.

The respective portions of each said adjustable electrode are preferablyseparated by a gap. The gap is preferably present on manufacture of theelectrode array. During implantation, the gap can be closed as theportions move towards one another. For example, if the carrier memberadopts a spirally curved configuration, the respective portions canundergo a change in orientation relative to the said common plane and socome into contact with each other.

In a further embodiment, the electrodes are formed from a biocompatibleconductive material such as platinum or iridium. The electrodes can beformed from a sheet of platinum or an alloy. The sheet or foil can havea thickness of between about 1, 2, 5 or 10 and 50 microns. Each formedelectrode can have a conducting portion extending away there from to alocation distal the electrode. Each portion of each of said adjustableelectrodes has at least one common conducting portion extending awaythere from. Each conducting portion can extend lineally away from itselectrode. The respective linear conducting portions are preferablyaligned in a parallel arrangement. The conducting portions arehereinafter referred to as “wires” as they serve to provide electricalconduction between each electrode to a location distal the electrodearray.

In a further embodiment, the electrodes and wires can be formed usingmachining processes as defined in International Patent Publication No WO02/089907 of the present applicant. For example, the electrodes andwires can be formed using electrical discharge machining (EDM), milling,cutting, or etching.

In another embodiment, the electrodes and wires can be formed usingconventional processes, such as those described in the Applicant's U.S.Pat. No. 6,421,569, the contents of which is incorporated herein byreference. In this regard, each of the electrodes can be a conductivepad, made from a suitable biocompatible material, such as platinum, withconventional wires welded to each of the electrodes providing electricalconduction between each electrode to a location distal the electrodearray. Each portion of each of the adjustable electrodes has at leastone conducting portion extending away there from.

In a preferred embodiment, the array comprises 30 electrodes, with thearray comprising at least 4 of said adjustable electrodes. Where thearray comprises 30 electrodes, the array can comprise 5 different setsof electrodes that have been formed individually and then stacked one ontop of the other to form a single electrode array. Where the arraycomprises 30 electrodes, the array can comprise 3 sets of sevenelectrodes, 1 set of 5 electrodes and 1 set of 4 adjustable electrodes.In this embodiment, the 3 sets of 7 electrodes are stacked one on top ofthe other, the set of 5 electrodes is stacked on these sets, with theset of 4 electrodes on top of the stack. Other combinations of sets can,however, be envisaged, for example 1 set of 3 electrodes with adjustableelectrodes at the tip to curve to a smaller radius, 1 set of 4, 1 set of5 & 3 sets of 6.

While the sets of electrodes are stacked one upon the other, it will beappreciated that the actual position of the electrodes in each set arenot necessarily vertically aligned. Rather, the set immediately aboveits lower set may be laterally offset so as to ensure the electrodes arevisible from beneath the stack.

The wires extending from each electrode are preferably of the samelength. It can, however, be envisaged that the wires could be formedwith different lengths to account for the ultimate offset present whenforming the stack.

Once the stack is formed, the hitherto at least substantially planarelectrodes are preferably deformed so as to at least partially extendthrough a third dimension. In a preferred embodiment, each of theelectrodes is curved out of the plane of the wires for each set ofelectrodes. The curvature can be substantially semi-circular. A mandrelcan be used to form the curvature in the electrodes.

Once the electrodes have been deformed to have a substantiallysemi-circular curvature, each of the electrodes can be further foldedabout a longitudinal axis of the array. This folding of the electrodespreferably serves to bend the electrodes around the wires of the array.The electrodes can be folded individually, in small groups, or alltogether. In one embodiment, the electrodes are folded so as to define alumen that extends through the array.

Once the electrode array is complete it can be encapsulated in a furtherlayer of a biocompatible relatively insulating material to form theelectrode carrier member. In a preferred embodiment, the biocompatiblematerial can be a silicone, such as a flexible siliconeelastomer-Silastic. Silastic MDX 4-4210 is an example of one suitablesilicone for use in the formation of the carrier member. In anotherembodiment, the elongate carrier member can be formed from apolyurethane or similar material.

In another method, the body of the array can be formed, with the wiringthen adhered to the array before the electrodes are bent around thebody.

In one embodiment, the carrier member can be formed in a mould with thebiocompatible material allowed to set around the array. In thisembodiment, the electrodes are preferably positioned in the mould so asto not be coated with the biocompatible material. In one embodiment, thecarrier member can be moulded in a straight configuration. In anotherembodiment, the carrier member can be moulded in a curved configuration,such as a spirally-curved configuration.

In a preferred embodiment, the electrode array is for use as animplantable tissue-stimulating device. More preferably, thetissue-stimulating device is a cochlear electrode assembly, morepreferably an intracochlear electrode assembly.

In a preferred embodiment, the intracochlear electrode assembly is apart of an implanted component of a cochlear implant system. Theimplanted component further preferably comprises a receiver coil and ahousing for a stimulator device. The carrier member preferably extendsoutwardly from the housing of the stimulator device.

In a further embodiment, the leading end of the carrier member isinsertable into a cochlea of a recipient. The wires of the electrodearray preferably extend back towards the trailing end of the carriermember.

The wires preferably extend back to the housing to at least a firstfeedthrough in the wall of the housing. The wires are preferably exposedat or adjacent the trailing end to allow connection to the feedthroughs.In one embodiment, the feedthrough provides hermetic and insulatedelectrical connection for each wire extending from the electrodeassembly into the housing of the implantable component. Each feedthroughcan be formed using the method described in U.S. Pat. No. 5,046,242, thecontents of which are incorporated herein by reference.

In a preferred embodiment, the orientation of the carrier member as itis firstly inserted through a cochleostomy into the cochlea ispreferably substantially straight. More preferably, the implantableorientation is straight. Following completion of implantation, thecarrier member preferably adopts a spirally curved configuration that atleast substantially matches the spiral nature of the scala tympani ofthe human cochlea. The carrier member is preferably pre-formed with thisspiral configuration and is then straightened either during manufactureand packaging of the device or prior to implantation. The carrier memberis preferably held straight prior to and at least during the initialstages of implantation by a stylet. The stylet preferably extendsthrough a lumen of the carrier member such as the lumen described hereinthat is formed by the folding of the electrodes about the wires.

As the carrier member is inserted into the scala tympani of the cochlea,the degree of curvature required of the array becomes tighter if thearray is to be implanted to a desired depth within the cochlea. Theability of the portions of the leading end electrodes to adjust inorientation relative to each other during this process serves to allowthe carrier to adopt a tighter degree of curvature than would otherwisebe the case.

Further, the provision of electrode elements having portions that arecapable of adjusting in orientation relative to each other allowsconventional electrode arrays to become more flexible along theirlength. This improved flexibility is achievable without needing torevert to smaller electrode elements of reduced surface area, which mayreduce the ability of the electrode elements to provide optimumstimulation and broad current spread. Therefore, the present inventionpotentially opens up a new realm for electrode array design whereflexibility and stiffness of the array can be reduced without the needfor reducing the stimulating surface area of the array.

In a further embodiment, the housing is preferably implantable in arecess of the temporal bone adjacent the ear of the recipient that isreceiving the output of the implant system. The housing is preferablyformed from a biocompatible material or has a biocompatible coating. Thehousing can be coated with a layer of silicone or parylene.

As already discussed, the implantable component preferably alsocomprises a receiver coil. The receiver coil preferably comprises a wireantenna coil. The antenna coil can be comprised of at least one, andpreferably at least two, turns of electrically insulated platinum orgold wire tuned to parallel resonance by a capacitor internal to thehousing. The electrical insulation of the antenna coil can be providedby a flexible silicone moulding and/or silicone or polyurethane tubing.The external coil can be constructed in a similar fashion to theimplanted coil or have a different construction.

The antenna coil is preferably external of the housing. Electricalconnection between the antenna coil and componentry of the implantablecomponentry within the housing can be provided by two hermetic andelectrically insulated ceramic feedthroughs or an electrical conductor.The ceramic feedthroughs can be formed using the method described inabovementioned U.S. Pat. No. 5,046,242.

The antenna coil of the implantable component preferably acts as part ofthe radio frequency (RF) link to allow transcutaneous bidirectional datatransfer between the implantable component and external components ofthe cochlear implant system. The radio frequency signals can comprisefrequency modulated (FM) signals. While described as a receiver coil,the receiver coil can preferably transmit signals to the transmittercoil which receives the signals.

The link between the two coils also provides a means of powering thecomponentry of the internal component. Where the implantable componentfurther has an on-board or implantable power source, such as arechargeable battery, the link can provide a means of inductivelycharging the battery when required.

The implanted housing preferably contains, in addition to the stimulatordevice, a receiver device. The receiver device is preferably adapted toreceive signals from the external component.

The housing of the external component preferably houses a speechprocessor adapted to receive signals output by a microphone. In apreferred embodiment, the microphone can be mounted to the housing or anear hook member. Other suitable locations for the microphone and/or thehousing for the speech processor can be envisaged, such as a lapel ofthe recipient's clothing.

The speech processor encodes the sound detected by the microphone into asequence of electrical stimuli following given algorithms, such asalgorithms already developed for cochlear implant systems. The encodedsequence is transferred to the implanted receiver/stimulator deviceusing the transmitter and receiver coils. The implantedreceiver/stimulator device demodulates the FM signals and allocates theelectrical pulses to the appropriate attached electrode by an algorithmwhich is consistent with the chosen speech coding strategy.

The external component preferably further comprises a power supply. Thepower supply can comprise one or more rechargeable batteries. Thetransmitter and receiver coils are used to provide power viatranscutaneous induction to the implanted stimulator/receiver device andthe electrode array.

While the implant system can rely on external componentry, in anotherembodiment, the microphone, speech processor and power supply can alsobe implantable. In this embodiment, these components can be containedwithin a hermetically sealed housing or the housing used for thestimulator device.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, a preferred embodiment of the invention is nowdescribed with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of a platinum sheet depicting how different setsof electrodes and adjoining wires can be formed in a platinum sheetthrough appropriate machining;

FIGS. 1 a and 1 b are enlarged plan views and FIG. 1 c is an enlargedperspective view of adjustable electrodes for use in the array depictedin FIG. 1;

FIG. 2 is a plan view of stacked sets of electrodes of an electrodearray suitable for use in a cochlear implant system according to thepresent invention; and

FIG. 3 is a view of a carrier member with a stylet at least partiallyretracted thereby allowing the carrier member to adopt a more pronouncedcurvature.

PREFERRED MODE OF CARRYING OUT THE INVENTION

FIG. 1 depicts 5 different sets of electrodes and associated wires thathave been formed on a single sheet of platinum foil. This figure depictsthe electrode sets prior to them being trimmed from the platinum sheet.Each of the sets 51-55 have been formed in the sheet using electricaldischarge machining (EDM) as defined in International Patent PublicationNo WO 02/089907 described above.

Once each of the sets 51-55 are formed, each set can be trimmed from theplatinum sheet and stacked one above the other to form an aligned arrayof electrodes 41. In the embodiment depicted in FIG. 1, the electrodearray comprises 30 electrodes, with the array comprising 3 stacked setsof 7 electrodes (51-53), 1 set of 5 electrodes (54) above these, and 1set of 4 electrodes (55) on top of the stack.

While the sets of electrodes are stacked one upon the other, it will beappreciated that the actual position of the electrodes 41 from therespective sets are not necessarily vertically aligned. Rather, the setimmediately above its lower set may be laterally offset so as to ensurethe electrodes are visible from beneath the stack. A drawing depicting apart of an example of a longitudinal array of electrodes 41 according tothe present invention is depicted in FIG. 2.

As is depicted more clearly in FIG. 1 a, each of the electrodes 41 ofelectrode set 55 can be so-called split electrodes. Each electrode inthis set is comprised of a first portion 41 a and a second portion 41 b,with the portions being separated by a longitudinal gap 41 c. Onmanufacture, the portions 41 a, 41 b extend outwardly in a plane from acommon conducting portion or wire 42.

In another embodiment depicted in FIG. 1 b, the gap 41 c can be bridgedby a bridge member 41 d. As depicted, the bridge member 41 d can extendbetween the portions 41 a and 41 b at a location distal the commonconducting portion 42. While a single bridge member is depicted in FIG.1 b, more than one such bridge member could be present.

In another embodiment depicted in FIG. 1 c, the portions can be linkedby a region 41 e that closes the gap between the portions 41 a and 41 band which has a thickness less than that of the adjacent portions. Asdepicted, the region 41 e can have a substantially V-shapedcross-section, with the electrode preferentially bendable at thislocation. It will be appreciated that the region 41 e could only bridgea portion of the gap, for example, the region 41 e could bridge the gapadjacent or near the common conducting wire 42.

Each electrode 41 has an associated wire 42 that extends from itsrespective electrode at least towards the trailing end of the carriermember in which the electrode array is supported. As depicted in FIG. 1,each wire extends lineally away from its electrode in a parallelarrangement with adjacent wires.

While the depicted embodiments depict the electrodes and “wires” asbeing formed from the same sheet of platinum as that used to form theelectrodes, it will be appreciated that both the electrodes and wirescould be formed using conventional processes, such as those described inthe Applicant's U.S. Pat. No. 6,421,569, the contents of which isincorporated herein by reference, and still fall within the scope of thepresent invention. In this regard, each of the electrodes can be aconductive pad, made from a suitable biocompatible material, such asplatinum, with conventional wires welded to each of the electrodesproviding electrical conduction between each electrode to a locationdistal the electrode array. For example, FIG. 3 could be readilyinterpreted as depicting conductive platinum pads 41 to whichconventional wires are welded and which then extend back through thelength of the carrier member 60.

Once the stack is formed, the hitherto at least substantially planarelectrodes 41 are preferably deformed so as to at least partially extendin a third dimension. In a preferred embodiment, each of the electrodesis curved out of the plane of the wires 42 for each set of electrodes.The curvature can be substantially semi-circular. A mandrel can be usedto form the curvature in the electrodes.

Once the electrodes 41 have been deformed to have a substantiallysemi-circular curvature, each of the electrodes 41 are further foldedabout a longitudinal axis of the array 40. This folding of theelectrodes 41 serves to bend the electrodes around the wires 42 of thearray. The electrodes are preferably folded together and define a lumenthat extends through the array 40. An example of the curvature ofindividual electrodes is depicted in FIG. 3.

Once the electrode array 40 is complete it is encapsulated in a furtherlayer of a biocompatible relatively insulating material such as siliconeto form an electrode carrier member 60. Silastic MDX 4-4210 is anexample of one suitable silicone for use in the formation of the carriermember 60.

The step of forming the carrier member 60 can comprise mounting thearray in a mould and filling the mould with the silicone and allowing itto cure. In this arrangement, the electrodes are positioned in the mouldso as to not be coated with the silicone. In the arrangement depicted inFIG. 3, the carrier member is moulded in a spirally-curved configurationand preferentially adopts this configuration unless straightened by thepresence of a stylet or other straightening device. In FIG. 3, thedegree of curvature of the depicted carrier member is to be taken asillustrative only.

In FIG. 3, the stylet passes through a lumen in the carrier member 60formed by the folding of the electrodes 41 as defined above. When thecarrier member 60 is in the configuration depicted in FIG. 3, the stylethas been at least partially retracted to allow the carrier member 60 tobegin to adopt its preferred spirally curved configuration.

As the carrier member begins to curve, the adjustable nature of theelectrodes 41 adjacent the tip of the carrier 60 allows these electrodesto adjust in orientation relative to each other and so allows the arrayto adopt a tighter curvature than would otherwise by the case. Such anarrangement ensures that the stimulating surface area of the electrodeelements throughout the array can be kept relatively constant, therebyensuring a uniform current spread from each of the electrodes employedin the array, from the most basal electrode to the most apicalelectrode. This arrangement therefore overcomes the need to reduce thesurface area/size of the most apical electrodes to enable that region tobe at its most flexible to achieve a greater amount of curvature.

While the depicted embodiment has adjustable electrodes adjacent the tipof the carrier, the array could be constructed of adjustable electrodesand non-adjustable electrodes, with the adjustable electrodes formed inthe array at locations where that adjustability is a greaterrequirement. For example, each of 30 electrodes, or at least 20electrodes that will be typically positioned past the basal turn, can beadjustable.

Further, whilst the depicted embodiment has electrodes arranged with asubstantially semi-circular arc, the electrodes could be arranged in amore conventional substantially flat manner, such as that described inthe Applicant's U.S. Pat. No. 6,421,569. In this regard, the adjustableelectrodes still function to impart greater adjustability and/orflexibility in the appropriate regions of the array. Further, whilst thedepicted embodiment has the electrodes and wires constructed from theone piece, it is also envisaged that the electrodes and the wires couldbe separately constructed and welded into connection in a moreconventional manner.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

1. A cochlear implant comprising: a flexible elongate carrier membercomprising at least one stimulating split electrode, said splitelectrode comprising: a first electrode portion; a second electrodeportion adjacent to and spaced from said first electrode portion so asto define a gap therebetween, wherein said first electrode portion andsaid second electrode portion are adjustable in orientation relative toeach other; and a common conducting portion directly electricallyconnecting said first electrode portion to said second electrode portionregardless of relative orientation of said first and second portions. 2.The implant of claim 1, wherein said split electrode further comprises:at least one flexible bridge member extending though said gap, connectedto said first and second electrode portions, and wherein said bridgemember is configured to limit changes in said relative orientation ofsaid first and second portions.
 3. The implant of claim 2, wherein saidat least one flexible bridge member and said first and second electrodeportions have substantially the same thickness.
 4. The implant of claim2, wherein said first and second electrode portions are elongate havingsubstantially parallel longitudinal axes, and wherein said gap is anelongate gap having a longitudinal axis substantially parallel to saidlongitudinal axes of said electrode portions, and wherein said commonconducting portion and said bridge member are longitudinally spaced insaid gap.
 5. The implant of claim 4, wherein said gap comprises proximaland distal ends and wherein said common conducting portion is positionedproximate to said proximal end of said gap and wherein said bridgemember is positioned proximate said distal end of said gap.
 6. Theimplant of claim 1, wherein said split electrode further comprises: alinking member, extending through said gap and connected to said firstand second electrode portions, configured to substantially fill saidgap.
 7. The implant of claim 6, wherein said linking member has athickness that is less than a thickness of said first and secondelectrode portions.
 8. The implant of claim 6, wherein said first andsecond electrode portions are elongate having substantially parallellongitudinal axes, and wherein said gap is an elongate gap having alongitudinal axis substantially parallel to said longitudinal axes ofsaid first and second portions, and wherein said linking membercomprises an approximately linear groove extending substantiallyparallel to said longitudinal axis of said gap, said groove configuredto allow said split electrode to bend at said groove.
 9. The implant ofclaim 6, wherein said linking member, common conducting portion, firstelectrode portion and second electrode portion comprise regions of aunitary split electrode.
 10. The implant of claim 1, wherein said firstand second electrode portions are rectangular and longitudinally extendfrom said common conducting portion, and wherein said gap is arectangular elongate gap positioned between said first and secondrectangular electrode portions.
 11. An electrode assembly comprising: aflexible elongate carrier member comprising at least one stimulatingsplit electrode, said split electrode comprising: a first electrodeportion; a second electrode portion adjacent to and spaced from saidfirst electrode portion so as to define a gap therebetween, wherein saidfirst electrode portion and said second electrode portion are adjustablein orientation relative to each other; and a common conducting portiondisposed in said gap directly electrically connecting said firstelectrode portion to said second electrode portion while allowingspecified changes in relative orientation between said first and secondportions.
 12. The assembly of claim 11, wherein said split electrodefurther comprises: at least one flexible bridge member extending thoughsaid gap, connected to said first and second electrode portions, andwherein said bridge member is configured to limit changes in relativeorientation of said first and second portions to said specified changesin relative orientation of said first and second portions.
 13. Theassembly of claim 12, wherein said at least one flexible bridge memberhas a thickness substantially equal to that of said first and secondelectrode portions.
 14. The assembly of claim 12, wherein said first andsecond electrode portions are elongate having substantially parallellongitudinal axes, and wherein said gap is an elongate gap having alongitudinal axis substantially parallel to said longitudinal axes ofsaid first and second electrode portions, and wherein said commonconducting portion and said bridge member are longitudinally spaced insaid elongate gap.
 15. The assembly of claim 11, wherein said splitelectrode further comprises: a linking member extending through saidgap, connected to said first and second electrode portions, wherein saidlinking member is configured to substantially fill said gap.
 16. Theassembly of claim 15, wherein said linking member has a thickness lessthan a thickness of said electrode portions.
 17. The assembly of claim15, wherein said linking member, common conducting portion, firstelectrode portion and second electrode portion comprise regions of aunitary split electrode.
 18. The assembly of claim 11, wherein saidfirst and second electrode portions are rectangular and longitudinallyextend from said common conducting portion, and wherein said gap is arectangular elongate gap having a longitudinal axis substantiallyparallel to longitudinal axes of said first and second electrodeportions; wherein said linking member includes a substantially lineargroove extending substantially parallel to said longitudinal axis ofsaid gap configured to allow said split electrode to bend at saidgroove.
 19. The assembly of claim 11, further comprising: a plurality ofelectrodes comprising: said at least one split electrode; and two ormore electrodes having a single electrode portion, wherein said at leastone split electrode is interspersed between said two or more electrodeshaving a single portion.
 20. An electrode array for a tissue-stimulatingprosthesis, comprising: a plurality of stimulating electrodes, whereinat least one of said electrodes comprises: a common conducting portion;and at least two electrically connected electrode portions extendingoutwardly from said common conducting portion, wherein said at least twoelectrically connected portions are adjustable in orientation relativeto each other; and a region configured to link said electrode portionsthat hilly or substantially fills any gap between said electricallyconnected portions, and which has a thickness less than that of saidelectrically connected portions.
 21. The array of claim 20, wherein saidregion that fully or substantially fills any gap between said portionshas a substantially V-shaped cross-section configured to allow saidelectrode to bend at said cross section.
 22. An electrode array for atissue-stimulating prosthesis, comprising: a plurality of stimulatingelectrodes, wherein at least one of said electrodes comprises: a commonconducting portion; at least two electrically connected portionsextending outwardly from said common conducting portion to define a gaptherebetween, and adjustable in orientation relative to each other; andone or more bridge members extending through said gap, connected to saidelectrode portions at a location distal said common conducting portion.23. The array of claim 22, wherein said one or more bridge members havea thickness equal to that of said electrode portions.
 24. An electrodeassembly for a tissue-stimulating prosthesis, comprising: at least onestimulating split electrode comprising: a first electrode region; asecond electrode region adjacent to and spaced from said first electroderegion, wherein said first electrode region and said second electroderegion are adjustable in orientation relative to each other; an elongateintermediate region positioned between said first and second electroderegions configured to separate said electrode regions; and a commonconducting region directly electrically connecting said first electroderegion to said second electrode region regardless of relativeorientation of said first and second electrode regions.
 25. Theelectrode assembly of claim 24, wherein said intermediate regioncomprises a gap, and wherein at least one flexible bridge connected tosaid first and second electrode regions extends through said gap. 26.The electrode assembly of claim 25, wherein said at least one flexiblebridge member and said first and second electrode regions havesubstantially the same thickness.
 27. The electrode assembly of claim25, wherein said first and second electrode regions have substantiallyparallel longitudinal axes, and wherein said gap is an elongate gaphaving a longitudinal axis substantially parallel to said longitudinalaxes of said electrode regions, and wherein said common conductingregion and said bridge member are longitudinally spaced in said gap. 28.The electrode assembly of claim 24, wherein said intermediate regioncomprises: a linking region connected to said first and second electroderegions, said linking region configured to permit said split electrodeto bend at said linking region
 29. The electrode assembly of claim 28,wherein said linking region has a substantially V-shaped cross-section.30. The electrode assembly of claim 28, wherein said first and secondelectrode regions have substantially parallel axes, and wherein saidlinking region has a longitudinal axis substantially parallel to saidlongitudinal axes of said first and second regions, and wherein saidlinking region includes an approximately linear groove extendingsubstantially parallel to said axis of said linking region configured toallow said adjustable electrode to bend at said groove
 31. The electrodeassembly of claim 28, wherein said linking region has a length that issubstantially the same as the lengths of said first and second electroderegions.